where AS was the absorbance value of the sample solution, and AB was that of the blank solution.
2.6. DPPH radical (DPPHradical dot) scavenging activity assay
DPPHradical dot scavenging activity assay was determined using a method modified from Brand-Williams, Cuvelier, and Berset (1995). Briefly, 0.5 mL of 1.4 mg/mL of the PSPA extract, or 1.4 mg/mL VC were added to 1.5 mL of 32.4 mM DPPHradical dot solution in ethanol representing the sample or a positive control, respectively. The mixture was shaken and allowed to stand at 23 °C in the dark for 30 min before measuring the absorbance at 517 nm. A mixture of 0.5 mL ethanol and 1.5 mL DPPHradical dot solution was used as the blank. The DPPHradical dot scavenging activity was calculated using the equation: